1. Technical Field
This invention relates generally to graphical processing in real-time operating systems adapted for high performance applications, such as those executing in a home communications terminal (HCT) to provide cable television or other audiovisual capabilities. More particularly, the invention provides a feature which improves the performance of operating systems installed in devices having limited computing resources.
2. Related Information
Conventional operating systems for HCTs, such as those in cable television systems, have typically provided limited capabilities tailored to controlling hardware devices and allowing a user to step through limited menus and displays. As growth in the cable television industry has fostered new capabilities including interactive video games, video-on-demand, downloadable applications, higher performance graphics, multimedia applications and the like, there has evolved a need to provide operating systems for HCTs which can support these new applications. Additionally, newer generations of fiber-based networks have vastly increased the data bandwidths which can be transferred to and from individual homes, allowing entirely new uses--such as telephony--to be developed for the HCTs. As a result, conventional HCTs and their operating systems are quickly becoming obsolete. In short, HCTs need to evolve to transform today's consumer television sets into interactive multimedia entertainment and communication systems.
Conventional display systems in HCTs include a host processor coupled to a video display device. Faster host processors generally provide faster display manipulations. However, with the advent of higher resolution screens, the amount of display information that needs to be processed also increases. Accordingly, merely increasing the host processor throughput may not be an optimal solution for increasing display performance.
Moreover, merely adding additional processors and memory to an HCT design may unacceptably increase its cost. Accordingly, it is desirable to find ways of increasing display performance within the framework of a low-cost design.
Conventional graphics systems allow groups of pixels to be moved in display memories in a single operation. The movement of at least two pixels together is commonly referred to in the art as bit block transferring (or BitBLT). Using a BitBLT, a CPU can select a block (most often, a rectangular block) of pixels, provide source and destination starting addresses, and invoke a hardware-supported function to perform the transfer. However, where multiple groups of pixels must be moved, the CPU is unnecessarily interrupted to start a new transfer and to update the source and destination addresses for the transfers.
Another inefficiency in conventional video display systems concerns the performance of a video capture function. For such a function, portions of a first memory area are repeatedly copied to a second area for display. As with conventional BitBLT operations, constantly interrupting a CPU to coordinate this function robs performance from the CPU.
In short, conventional video display systems such as those in an HCT suffer from performance inefficiencies which hinders their use for new applications.